Process to detect and count yarn defects having a color background and a camera

ABSTRACT

A process and device to detect and count yarn defects in a yarn segment including a camera (5), a computer (8) and an image processing program. The yarn (30) is illuminated with an intensity dependent upon the thickness of the yarn (30) and is photographed by the camera (5). The photographed image is digitalized in the computer with the image processing program and low-contrast points are filtered out. The remaining points are gathered together into coherent areas the sizes of which are classified into predetermined size classes and are stored.

BACKGROUND OF THE INVENTION

Gravimetric processes and manual counting processes were known in thepast for the detection of yarn defects caused by impurities. Gravimetricprocesses are based on the collection and weighing of eliminated trashparticles during the spinning process, e.g. on a rotor spinning machine.This does however not indicate how much trash still remains in thefinished yarn nor the type of impurities remaining.

Also known are manual counting processes to ascertain how many trashparticles are in the yarn. For this purpose the spun yarn is knit on acircular knitting machine and a certain surface is cut out of the knitmaterial. A grid is placed on the cut-out surface and the number oftrash particles in the individual areas is counted. The disadvantage ofthis system is the great amount of time necessary to prepare the knitmaterial and then to count the particles. It is also a disadvantage thatthe success of the process depends very much on the accuracy of persondoing the counting. Comparisons have shown that examinations of the sameknit material by different persons show very different counting results.

OBJECTS OF THE INVENTION

It is a principal object of this invention to create a rapid, objectiveand reproducible method to count the trash particles and other yarndefects or impurities in the yarn. Additional objects and advantages ofthe invention will be set forth in part in the following description, ormay be obvious from the description, or may be learned through practiceof the invention.

Advantageous embodiments of the invention are shown in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a layout of the devices used for optical yarn analysis;

FIG. 2 shows a measuring instrument for yarn analysis;

FIG. 3 shows a winding device;

FIG. 4 shows a flow-chart for the control of the device for optical yarnanalysis; and

FIG. 5 shows the results of a trash analysis of the yarn.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the presently preferredembodiments of the invention, one or more examples of which areillustrated in the accompanying drawings. Each example is provided byway of explanation of the invention, and not as a limitation of theinvention. For instance, features illustrated or described as part ofone embodiment can be used on another embodiment to yield a stillfurther embodiment. Additionally, the numbering of components in thedrawings is consistent throughout the application, with the samecomponents having the same number in each of the drawings.

FIG. 1 shows a schematic sketch of a device for optical yarn analysis.The yarn to be examined is wound up on a bobbin 1. For the examinationthe yarn is introduced through an opening into a housing 2. In order toavoid influences due to external light, the housing 2 is madelight-tight in an advantageous embodiment. This ensures that a wind-upunit 3 can be illuminated evenly in incident light by a light source 4.The light-tight housing 2 prevents any additional light sources frominfluencing the wind-up unit 3 from the outside and thus possibly tocast shadows which the system would erroneously recognize to be yarndefects. The wind-up unit 3 is either a conventional yarn plate or anautomatically driven device according to the invention such as describedin further detail in FIGS. 2, 3, and 4.

The light source 4 in this case is advantageously a fluorescent bulb.Two concentric ring-shaped fluorescent bulbs have shown to be especiallywell suited here. Such a light source 4 ensures even, shadowlessillumination of a testing surface on the wind-up unit 3. If the lightsource 4 is an infrared light, trash and other yarn irregularities whichare inside the yarn, and not only those located on the outside and onthe visible side of the yarn, can be detected. A camera 5 is installedabove the light source 4. This is preferably a CCD camera. CCD camerashave the advantage that they are able to take a picture very precisely,are insensitive to electromagnetic interference radiations, and produceno drop-off of luminosity towards the edge of the picture. Very briefexposure times are sufficient with a CCD camera. However longer exposuretimes still do not cause the photographed scene to be burned in on thetarget of camera 5. Cameras of this type can therefore be used incontinuous operation over very long periods of time while optimal imagequality is maintained.

The camera 5 is connected via a camera controller 6 to a computer 8. Thepower supply for the CCD camera 5 as well as selection of the type ofoperation are located in the camera controller 6.

The wind-up unit 3 is connected to the computer 8 via a wind-up control7. The wind-up control 7 determines when and how the winding of thewind-up unit 3 is to be modified. The individual control processes areshown in greater detail in FIG. 4.

To display the yarn defects detected in the yarn analysis device, agraphics screen 9 and a printer 10 are connected to the computer 8. Theimage photographed by the camera 5 is reproduced on the graphics screen9. The different detected yarn defects are marked on the graphics screen9 so that the operator is able to ascertain whether particles, and ifany, which particles were detected by the system, in particular in orderto adjust the device. If the operator sees that impurities in yarn 30which are visible to the naked eye are not recognized by the system,finer tuning is required in order to modify the system's trash particlerecognition. The results of the analysis can be printed out on theprinter 10.

Instead of the yarn 30 from bobbin 1 and from the wind-up unit 3, it isalso possible to present a woven or knit material to the yarn analysissystem to be analyzed. A presentation for analysis of this type alsofalls within the framework of the invention.

FIG. 2 shows the basic layout of the measuring instrument contained inhousing 2. The camera 5 and the light source 4 are fastened to a stand11. In an advantageous embodiment, the lens of the camera 5 is pointingthrough the center of two concentric fluorescent lights of differentdiameter. The intensity of the light source can be changed by means of adimmer. Intensities between 700 lux and 1600 lux have proven to beadvantageous, with thicker yarns requiring the greater intensities.

The light source can also consist of a homogenous illumination placed atthe side of the measuring instrument. The illumination of the measuredsurface may be ensured by a semi-permeable mirror which directs thelight rays upon the measured surface on the one hand, and makes itpossible on the other hand to take the picture by means of the camera.

The camera 5 is aimed at an area between two rollers 15, 16 betweenwhich a background surface used as a contrast surface 18 is placed. Theyarn 30 is located between the camera 5 and the contrast surface 18, ata short distance from the contrast surface 8.

The yarn 30 is conveyed to the measuring instrument via a yarn brake 12.This ensures that sufficient tension is always present in the yarn 30.Following the yarn brake 12, a yarn monitor 13 is provided in the pathof yarn 30. The yarn monitor 13 verifies the presence of the yarn 30. Assoon as the yarn monitor 13 ascertains that no more yarn is beingconveyed to the measuring instrument, it automatically shuts off themachine. In order to ensure orderly transportation to the contrastsurface 18, a guiding eyelet 14 is provided directly before the roller15. The yarn 30 runs through this guiding eyelet 14 and over roller 15into a dividing mechanism 17 and then over roller 16. The yarn 30 isdeflected at the roller 16 and is taken back to the roller 15. As itpasses again through the dividing mechanism 17, a defined distance fromthe preceding yarn winding is maintained. This winding around therollers 15 and 16 with the passage through the dividing mechanism 17 isrepeated until a sufficiently large yarn surface is provided to beacquired by the camera 5. It has proven to be advantageous for themeasuring field to be slightly larger than the filed photographed by thecamera 5, as in that case uneven illumination at the edge of themeasuring field or unwanted light intrusions are eliminated.

To photograph the yarn wound around rollers 15 and 16, a measuring fieldwith dimensions of approximately 55×40 mm has been shown to beadvantageous. With a distance between the individual yarn windings ofapproximately 0.7 mm, approximately 3 m of the yarn 30 are measured perphotograph.

After the last winding, the yarn 30 is led off roller 16 through a yarnmonitor 20. This yarn monitor 20 verifies the presence of the yarn asdoes the yarn monitor 13. If the yarn monitor 20 does not register thepresence of yarn, this is a signal for the measuring instrument that theyarn withdrawal is not taking place in a correct manner. The measuringinstrument is then switched off. The yarn 30 runs through a guidingeyelet 21 following the yarn monitor 20. The guiding eyelet 21 ensuresthat the yarn 30 is fed correctly to a draw-off device with a pressureroller 22 and a draw-off roller 23. The yarn 30 which leaves themeasuring instrument via the draw-off device is conveyed to a yarnsucking pipe 25 in the embodiment shown. The yarn sucking pipe 25 guidesthe yarn 30 into a waste container which is not shown here. It ishowever also possible to feed the yarn 30 to a reeling device instead ofthe waste container and to wind it up on a bobbin.

The roller 15 is advantageously made in the form of a friction roller.This means that it is not driven autonomously but is rotated by the yarnwindings which surround it and move as a new yarn grouping is broughtinto position to be measured. The roller 16 however is an autonomouslydriven roller. Here it assists the forward motion of the yarns throughthe draw-off device.

The dividing mechanism 17 is placed between the rollers 15 and 16. In anadvantageous embodiment, the dividing mechanism 17 consists of aplurality of disks in a row, each being separated from the other by aspacer of lesser diameter.

Blowing nozzles 19 are placed between the parallel yarn windings and thecontrast surface 18. The contrast surface 18 is cleaned before eachmeasuring process by means of the blowing nozzles 19 which are directedupon the top of the contrast surface 18. In this manner an erroneousindication of the measuring instrument due to dirt on the contrastsurface 18 is avoided.

The driven roller 16 is connected via a toothed belt 24 to the draw-offroller 23 of the draw-off device. Thus, synchronized movement is ensuredin a simple manner between roller 16 and draw-off roller 23. This isnecessary to avoid yarn breakage in the measuring instrument. Acontrolled transmission between the driven roller 16 and the draw-offroller 23 can cause the draw-off roller 23 to convey the yarn 30 at thesame speed as in the winding device. The yarn 30 is thereby constantlyheld under tension in the wind-up unit 3, so that no distortion willoccur as the yarn grouping is received in the measuring field. Thepre-stressing of a spring causes the pressure roller 22 to be pressedagainst the draw-off roller 23 and ensures slip-free withdrawal of yarn30.

FIG. 3 shows a top view of a wind-up unit 3. A contrast surface 18 islocated between the rollers 15 and 16. If the yarn 30 is examined fortrash contents, it has been shown to be advantageous to use a whitecontrast surface 18, as the white yarn recedes optically in that case bycomparison to the dark trash. If however light yarn defects which arenot caused by trash are to be found in the yarn, a black background isadvantageous to bring out these defects.

The contrast surface 18 can be subjected to lateral blowing by nozzles19 for cleaning purposes. The yarn windings wound around the rollers 15and 16 can be recognized above the contrast surface 18. For this purposethe yarn 30 is fed on the side of the non-driven roller 15 to themeasuring instrument and is withdrawn form the measuring instrument bythe draw-off device on the side of the driven roller 16. The division ofthe individual windings is maintained constant by the dividing mechanism17. The roller 15 is over-mounted in a bearing 28. An initiator 29 isprovided on the roller 15 to ascertain whether the reeling device isstopped and whether the yarn 30 is thereby correctly positioned to bephotographed by the camera 5.

The roller 16 is over-mounted in a bearing 26. The roller 16 is drivenby a motor 27. A permanently excited d.c. servomotor with a maximumrotational speed of 6000 l/min has shown to be advantageous. With such amotor, precise starting of defined segments of the yarn windings isachieved.

A field 31 is shown on the contrast surface 18. The field 31 defines thesurface in which the camera 5 takes a picture. By driving the yarn 30 bymeans of motor 27, the photographed yarn grouping is moved out of field31 and a new yarn grouping or a new segment of the yarn grouping isready in the field 31 to be photographed. It has been shown to beadvantageous for the field 31 to be of such a size that a completewinding volume without overlapping is recorded with each photograph witha five-time shift of the yarn grouping. This ensures a nearlyuninterrupted, and in any case non-multiple recording of the yarn lengthwhich is present in the wind-up unit 3. After completion of a sequenceof 5 photographs, the entire yarn length wound around the rollers 15 and16 is measured by the measuring instrument. For this purpose, the entirephotographed yarn length is reeled through until a new length of yarn isavailable to be photographed. This is necessary in order to avoid havingthe same yarn segments analyzed twice by the measuring device, thusproducing misreadings in the measuring process.

FIG. 4 shows a flow-chart for the control of the wind-up unit 3. Thesystem receives a starting signal via input E1. A determination is madein preselection counter 2, as to the number of photographs after whichthe automatic measuring sequence is to be stopped. It can be adjusted atthe user level in computer 8. In a preselection counter 1, thedetermination is made as to how many photographs are to be taken beforea new wind-up operation is to take place. It has been shown to beadvantageous for this counter to set at the number 5. This preselectioncounter means that 5 photographs are taken in order to cover the entirevolume of windings. In the example shown, this counter can be changedonly in the program, and not at the user level. This counter is ofcourse also dependent on the size of the measuring field 31 to bemeasured, as well as on the size of a yarn winding. The length of themeasuring field 31, multiplied by the preselection counter 1, shouldgive substantially the length of the winding. This ensures that thewound-up yarn is examined essentially over its entire length.

If the controls find that no yarn is present at the input E2, theprogram is stopped. If the signal indicating the presence of yarn isreceived by the input E2, a verification is carried out to find outwhether the initiator 29 is vaporized or not. This signal is transmittedto the controls via input E3. If the initiator 29 is not vaporized, i.e.if the yarn winding is not positioned at a predetermined location, asignal is transmitted to an output A1 to switch motor 27 to creep speed.The system then queries again whether the initiator 29 is vaporized. Assoon as this is done a signal is transmitted to the output A1 indicatingthat the creep sped of the motor is to be switched off. After a waitingperiod of approximately 0.5 seconds which is provided for the yarn tosettle down after coming into the desired position, a photograph istaken. After this photograph, a waiting period 2 of e.g. approx. 5seconds is initiated. This waiting period 2 is used to process thepicture. During that time the image recorded by the camera 5 is preparedfor further processing and for analysis in an image processing system.

At the end of the waiting period 2, the preselection counter 2 whichindicates the total number of photographs of the automatic measuringprocess is set back by one. As soon as the preselection counter 2 hasreached value 0 the program is stopped. If the preselection counter 2has not yet reached value 0, the preselection counter 1 which is set tothe value 5, as described above for the shown embodiment, is set back byone. As long as the preselection counter 1 has not yet reached value 0the creep speed of the motor 27 is switched on and the process startsagain with the query of input E2.

If however the value of the preselection counter 1 is 0, a signal istransmitted via output A2 to the motor 27, prompting the latter toproduce a new winding of the wind-up unit 3 by running at the mainwinding speed. The motor 27 runs for a predetermined period of time forthe new winding. This period of time depends on the size of the wind-upunit 3 and must in any case be of sufficient duration for the wind-upunit 3 to be covered with new yarn 30. During the running of motor 27 atmain winding speed, the input E2 is queried on the presence of a yarn.If no yarn is present, i.e. if a yarn breakage has occurred, the programis stopped. At the end of the winding period the motor 27 is stopped.The preselection counter 1 is again set to value 5 and the programstarts anew.

FIG. 5 shows an evaluation of an analyzed yarn. In this analysis theyarn was examined for its trash contents. The found trash particles weredivided into different size classes. The first 12 size classes containtrash particles measuring from 0 to 12 mm², with each size classcovering a range of 0.1 mm². In this example, the sizes of trashparticles in size class 13 range from 1.2 to 5 mm². The analysis showsthat most trash particles were found in size class 2. In order tosimplify the information on trash contents in the yarn, these 13 sizeclasses were subdivided into 3 characteristic classes. Class A in thiscase contains the small trash particles, class B the medium-size trashparticles and class C the large trash particles.

In order to ascertain the size of trash particles found, a calibrationof the system must be carried out at the beginning of the analysisprocess. This means that a predetermined size is provided with theappropriate scale and is entered into the system so that the latter mayascertain the size of the found trash particles and classify themaccordingly into their size classes.

The detection of the trash particles is based on different graygraduations which the system recognizes. It has been shown to beadvantageous to use an image processing device capable of distinguishing256 grey graduations. In order to define which grey tones should berecognized by the image processing device as being trash particles, acertain threshold value of the grey graduations is set in the program.

By setting the given threshold value, the system is caused to blur thedifference between the yarn grouping and the background surface so thatonly the dark trash particles can be recognized. The threshold value isadjusted so that all the trash particles if possible can be recognizedon the graphic screen. The linked points, so-called pixels, which arerecognized as trash particles are gathered together as surfaces in thecomputer, are sorted according to size and are classified into thedifferent size classes and are stored.

The process and the device can be used in particular for quality controlof a produced yarn or to detect adjustment errors in the spinningmachine. It has furthermore been proven to be advantageous indetermining the utilization of the correct raw material. Such adetection of yarn defects ensures advantageous further processing of theyarn.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope or spirit of the invention. Thus, it isintended that the present invention cover such modifications andvariations as come within the scope of the appended claims and theirequivalents.

We claim:
 1. A process for detecting and counting yarn defects in a yarnsegment, said process comprising the steps of:disposing a segment ofpredetermined length of yarn in front of a predetermined backgroundsurface, the background surface being of a color to enhance thevisibility of yarn defects in the yarn; illuminating the segment of yarnin front of the background surface with an illumination intensity whichis dependent on the thickness or color of the yarn; photographing theyarn segment in front of the background surface with a camera anddigitizing the photographed image in a computer by way of an imageprocessing program; filtering out low contrast points from the digitizedimage which do not correspond to yarn defects; categorizing and sortingby predetermined size classes the remaining contrast pointscorresponding to yarn defects; and generating a readout of thecategorized yarn defects for subsequent analysis.
 2. The process as inclaim 1, further comprising cleaning the background surface before saidphotographing.
 3. The process as in claim 1, further comprisingilluminating the segment of yarn from above the background surface inthe direction of the camera.
 4. The process as in claim 1, furthercomprising illuminating the segment of yarn with a homogeneouslyradiating light source.
 5. The process as in claim 1, further comprisingilluminating the segment of yarn with an infrared lamp.
 6. The processas in claim 1, further comprising disposing the segment of yarn in frontof the background surface in the form of a processed yarn product. 7.The process as in claim 1, further comprising winding subsequentsegments of yarn from a bobbin for analysis so that a statisticalascertainment of the sum of yarn defects in the yarn on the bobbin isgenerated.
 8. The process as in claim 7, wherein each individual segmentof yarn in wound up in parallel windings in front of the backgroundsurface, in that a section of the parallel windings are photographed andthen conveyed beyond the background surface wherein a subsequentcontiguous segment of yarn is then wound up in parallel windings andanalyzed and so forth until a continuous predetermined length of yarnform the bobbin has been analyzed.
 9. A device for detecting andcounting yarn defects in yarn supplied from a bobbin, said devicecomprising:an apparatus for photographing and analyzing a segment ofpredetermined length of yarn; a first roller and a second roller placedat a distance from each other below said photographing apparatus, one ofsaid rollers being a driven roller, said rollers configured to conveycontinuous segments of yarn below said apparatus; and a parallel windingdevice configured with said rollers which directs said continuoussegments of yarn into parallel windings around said rollers, the rollersdisposed so that said parallel windings of yarn therebetween can bephotographed and analyzed by said photographing apparatus.
 10. Thedevice as in claim 9, further comprising a background surface disposedbetween said rollers at a height so as to be below the parallel windingsof yarn, said background surface comprising a color which enhancesdetection of defects in the yarn.
 11. The device as in claim 10, furthercomprising a cleaning device disposed to clean said background surface.12. The device as in claim 11, wherein said cleaning device comprises atleast one blowing nozzle directed upon said background surface.
 13. Thedevice as in claim 9, further comprising a yarn tensing device disposedbetween said bobbin and said first roller.
 14. The device as in claim 9,further comprising a yarn monitor disposed between said bobbin and saidfirst roller.
 15. The device as in claim 9, further comprising a yarndraw off device disposed after said second roller, said yarn draw offdevice configured to draw the parallel windings of yarn from saidrollers after they have been photographed.
 16. The device as in claim15, wherein said second roller comprises said driven roller, said yarndraw off device comprising a drive roller which is indirectly driven bysaid second roller.
 17. The device as in claim 15, further comprising ayarn monitor disposed between said second roller and said yarn draw offdevice.
 18. The device as in claim 16, further comprising an initiatordisposed generally at said first roller to signal yarn position.
 19. Thedevice as in claim 9, wherein said parallel winding device comprises aseparator disposed between said rollers.
 20. The device as in claim 9,further comprising a background surface disposed between said rollers,and wherein said photographing apparatus comprises a camera disposedabove said background surface.
 21. The device as in claim 20, furthercomprising a light source disposed above said background surface. 22.The device as in claim 21, wherein said light source has a variableintensity.
 23. The device as in claim 21, wherein said light sourcecomprises a homogeneous light.
 24. The device as in claim 21, whereinsaid light source comprises an infrared lamp.
 25. The device as in claim20, further comprising a light-tight housing, said rollers, backgroundsurface, and cameral disposed within said housing.